The present invention relates generally to a propeller shaft for a motor vehicle, and a universal joint adapted to such a propeller shaft.
A typical propeller shaft of a motor vehicle is composed of two or three separate shafts which include a drive shaft linked to a transmission side, and a driven shaft linked to a differential gear side. This propeller shaft is provided with a Cardan type universal joint to join one longitudinal end of one of the separate shafts with one longitudinal end of another.
Japanese Patent Application Publication No. 2009-047181 discloses such a universal joint. The universal joint includes: a cross shaft member including four shaft parts forming a cross-shape; and four bearing cups each of which has a hollow-cylindrical shape having a bottom and is rotatably mounted to a corresponding one of the shaft parts through a needle bearing disposed between an inner peripheral surface of the each bearing cup and an outer peripheral surface of the corresponding shaft part.
Each shaft part of the cross shaft member includes an oil hole inside, which extends in the longitudinal direction of the shaft part and allows lubricating oil such as grease to flow in the longitudinal direction of the shaft part. The inner bottom surface of each bearing cup includes a central circular recess which faces and communicates with the oil hole, and further includes oil grooves each of which extends radially outwardly from the circular recess and communicates with the circular recess.
In the configuration described above, lubricating oil flows through the oil hole of the shaft portion of the cross shaft member to the inner bottom surface of the bearing cup along with rotation of the propeller shaft, and then flows from the circular recess through the radial oil grooves to the needle bearing side, and thereby holds lubricated the boundary between the distal end surface of the shaft part and the inner bottom surface of the bearing cup.